Editing Marine mammal (section)

====Ocean traffic and fisheries====
{{further|Cetacean bycatch}}
[[File:Eubalaena glacialis dead.jpg|thumb|right|The remains of a [[North Atlantic right whale]] after it collided with a ship [[propeller]]|alt=A right whale sliced on both sides after colliding with a boat. A large amount of its flesh is visible as well as the intestines floating in the water]]
[[By-catch]] is the incidental capture of non-target species in [[fisheries]]. Fixed and drift [[gill net]]s cause the highest [[Mortality rate|mortality]] levels for both cetaceans and pinnipeds, however, entanglements in long lines, mid-water trawls, and both trap and pot lines are also common.<ref>Perrin, W. F. (1994) "Status of species" in Randall R. Reeves and Stephen Leatherwood (eds.) ''Dolphins, porpoises, and whales: 1994–1998 action plan for the conservation''. Gland, Switzerland: International Union for Conservation of Nature and Natural Resources</ref> [[Tuna]] [[Seine fishing|seines]] are particularly problematic for entanglement by dolphins.<ref>{{Cite journal | doi = 10.1023/A:1008854816580|title=An ecological view of the tuna—dolphin problem: impacts and trade-offs| year = 1998|url=https://www.researchgate.net/publication/227263116| last1 = Hall | first1 = M. A. | journal = Reviews in Fish Biology and Fisheries| volume = 8| pages = 1–34|s2cid=32946729}}{{open access}}</ref> By-catch affects all cetaceans, both small and big, in all habitat types. However, smaller cetaceans and pinnipeds are most vulnerable as their size means that escape once they are entangled is highly unlikely and they frequently drown.<ref name=clap/> While larger cetaceans are capable of dragging nets with them, the nets sometimes remain tightly attached to the individual and can impede the animal from feeding sometimes leading to [[starvation]].<ref name=clap/> Abandoned or lost nets and lines cause mortality through ingestion or entanglement.<ref name="and">{{cite journal|jstor=1383601|title=Marine Mammals in the Next One Hundred Years: Twilight for a Pleistocene Megafauna?|last=Anderson, Paul K. |journal=Journal of Mammalogy|volume=82|issue=3|year=2001|pages=623–629|doi=10.1093/jmammal/82.3.623}}</ref> Marine mammals also get entangled in [[aquaculture]] nets, however, these are rare events and not prevalent enough to impact populations.<ref name="wur">{{cite book|last1=Wursig|first1= Bernd|last2=Gailey|first2=Glenn A.|year=2002|chapter=Marine Mammals and Aquaculture: Conflicts and Potential Resolutions|editor1-first=Robert R.|editor1-last=Stickney|editor2-first=James P.|editor2-last=McVey|title=Responsible marine aquaculture|location=Wallingford, Oxon; New York|publisher=CABI|isbn=978-0-85199-604-2|oclc=228169018}}</ref>

Vessel strikes cause death for a number of marine mammals, especially whales.<ref name=clap/> In particular, fast commercial vessels such as [[container ship]]s can cause major injuries or death when they collide with marine mammals. Collisions occur both with large commercial vessels and [[recreational boat]]s and cause injury to whales or smaller cetaceans. The critically endangered [[North Atlantic right whale]] is particularly affected by vessel strikes.<ref>{{cite journal|first1=P. B.|last1=Conn|first2=G. K.|last2=Silber|year=2013|title=Vessel speed restrictions reduce risk of collision-related mortality for North Atlantic right whales|journal=Ecosphere|volume=4|issue=1|doi=10.1890/ES13-00004.1|pages=art43|doi-access=free}}{{open access}}</ref> [[Tourism]] boats designed for whale and [[dolphin watching]] can also negatively impact on marine mammals by interfering with their natural behavior.<ref name="const">{{Cite journal | doi = 10.1016/j.biocon.2003.12.009| title = Dolphin-watching tour boats change bottlenose dolphin (''Tursiops truncatus'') behaviour| journal = Biological Conservation| volume = 117| issue = 3| pages = 299–307| year = 2004| last1 = Constantine | first1 = R. | last2 = Brunton | first2 = D. H. | last3 = Dennis | first3 = T. | bibcode = 2004BCons.117..299C}}</ref>

The fishery industry not only threatens marine mammals through by-catch, but also through competition for food. Large-scale fisheries have led to the depletion of [[fish stocks]] that are important prey species for marine mammals. Pinnipeds have been especially affected by the direct loss of food supplies and in some cases the harvesting of fish has led to food shortages or dietary deficiencies,<ref>{{Cite journal |doi=10.1139/z00-060 |title=Pollock and the decline of Steller sea lions: Testing the junk-food hypothesis |journal=Canadian Journal of Zoology |volume=78 |issue=7 |pages=1243–1250 |year=2000 |last1=Rosen |first1=D. A. |last2=Trites |first2=A. W. }}</ref> starvation of young, and reduced recruitment into the population.<ref>{{Cite journal | doi = 10.1111/j.1748-7692.1999.tb00857.x| title = Increase in Extralimital Occurrences of Ice-Breeding Seals in the Northern Gulf of Maine Region: More Seals or Fewer Fish?| journal = Marine Mammal Science| volume = 15| issue = 3| pages = 906–911| year = 1999| last1 = McAlpine | first1 = D. F. | last2 = Stevick | first2 = P. T. | last3 = Murison | first3 = L. D. | bibcode = 1999MMamS..15..906M}}</ref> As the fish stocks have been depleted, the [[competition]] between marine mammals and fisheries has sometimes led to conflict. Large-scale [[culling]] of populations of marine mammals by commercial fishers has been initiated in a number of areas in order to protect fish stocks for human consumption.<ref>{{cite journal|last=Hutchins, J. |year=1996|title=Spatial and temporal variation in the density of northern cod and a review of hypotheses for the stock's collapse|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume= 53|issue=5|pages=943–962|doi=10.1139/cjfas-53-5-943|url=http://people.uncw.edu/scharff/courses/458/Discussion%20articles/Hutchings%201996%20-%20review%20of%20the%20cod%20collapse.pdf}}{{open access}}</ref>

Shellfish aquaculture takes up space so in effect creates competition for space. However, there is little direct competition for aquaculture shellfish [[harvest]].<ref name=wur/> On the other hand, marine mammals regularly take [[finfish]] from farms, which creates significant problems for marine farmers. While there are usually legal mechanisms designed to deter marine mammals, such as anti-predator nets or harassment devices, individuals are often illegally shot.<ref name=wur/>